Conductive interconnect structures and formation methods using supercritical fluids

ABSTRACT

Conductive interconnect structures and formation methods using supercritical fluids are disclosed. A method in accordance with one embodiment of the invention includes forming a via in a substrate, with the via having a width and a length generally transverse to the width, and with a length being approximately 100 microns or more. The method can further include disposing a conductive material in the via while the via is exposed to a supercritical fluid. For example, copper can be disposed in the via by introducing a copper-containing precursor into the supercritical fluid and precipitating the copper from the supercritical fluid. Interconnect structures can be formed using this technique in a single generally continuous process, and can produce conductive structures having a generally uniform grain structure across the width of the via.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No. 11/169,838 filed Jun. 28, 2005, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention is directed generally toward conductive interconnect structures and formation methods using supercritical fluids.

BACKGROUND

Microelectronic imagers are used in digital cameras, wireless devices with picture capabilities, and many other applications. Cell phones and Personal Digital Assistants (PDAs), for example, are incorporating microelectronic imagers for capturing and sending pictures. The growth rate of microelectronic imagers has been steadily increasing as they become smaller and produce better images with higher pixel counts.

Microelectronic imagers include image sensors that use Charged Coupled Device (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS) systems, or other solid-state systems. CCD image sensors have been widely used in digital cameras and other applications. CMOS image sensors are also quickly becoming very popular because they are expected to have low production costs, high yields, and small sizes. CMOS image sensors can provide these advantages because they are manufactured using technology and equipment developed for fabricating semiconductor devices. CMOS image sensors, as well as CCD image sensors, are accordingly “packaged” to protect their delicate components and to provide external electrical contacts.

FIG. 1A is a partially schematic illustration of an imaging device 10 configured in accordance with the prior art. The imaging device 10 includes a die 20 having an integrated circuit 21 coupled to an image sensor 12. A color filter array (CFA) 13 is formed over the active pixels of the image sensor 12. The CFA 13 has individual filters or filter elements configured to allow the wavelengths of light corresponding to selected colors (e.g., red, green, or blue) to pass to each pixel of the image sensor 12. A plurality of microlenses 14 form a microlens array 15 that is positioned over the CFA 13. The microlenses 14 are used to focus light onto the initial charge accumulation regions of the image sensor pixels. A glass cover 16 is positioned to protect the microlens array 15 and other features of the die 20 from contamination. A device lens 17 is positioned a selected distance from the microlens array 15 to focus light onto the microlens array 15 and ultimately onto the image sensor 112.

The integrated circuit 21 of the die 20 can be electrically coupled to external devices via solder balls 11. The solder balls 11 are located on the side of the die 20 opposite from the image sensor 12 so as to avoid interference with the operation of the image sensor 12. Accordingly, the die 20 can include multiple through-wafer interconnects (TWIs) connected between the solder balls 11 and the bond pads 22, which are in turn connected to the integrated circuit 21. Each TWI can include a via that extends through the die 20, and an electrically conductive interconnect structure 30 located in the via.

FIG. 1B is an enlarged, cross-sectional view of an interconnect structure 30 configured in accordance with the prior art. The interconnect structure 30 includes a via 50 that extends through the bond pad 22 and through the die 20. A dielectric layer 31 electrically isolates the via 50 from other structures in the die 20, and a barrier layer 33 is positioned against the dielectric layer 31 to prevent migration of conductive materials away from the interconnect structure 30. A seed layer 34 and one or more conductive layers 37 (two are shown in FIG. 1B) are disposed on the barrier layer 33. These conductive layers can include materials such as copper and/or nickel. Nickel can be used as a second conductive layer to provide a barrier between a copper conductive layer and a volume of fill material 40. The fill material 40 typically includes solder.

One characteristic of the interconnect structure 30 is that the conductive layers 37 can have an uneven thickness. This is particularly so for interconnect structures having high aspect ratios (e.g., greater than 1:1). One drawback with this feature is that it may cause discontinuities in the electrical path between the bond pad 22 and the solder ball 11. Accordingly, the interconnect structure 30 may not always provide a reliable electrical connection between these two structures.

Another characteristic of the interconnect structure 30 is that the fill material 40 typically includes solder. The solder will only wet to a metal surface, and it will consume some of that surface during the wetting process. If the conductive layers 37 are nonexistent or so thin that they become consumed at the bottom of the via, then the solder fill material 40 may lose its adhesion to the sidewall in this region of the via. This in turn may result in a failure of the electrical path between the bond pad 22 and the solder ball 11.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B illustrate an imaging device formed by a process in accordance with the prior art.

FIG. 2 is a flow diagram illustrating a process for forming interconnect structures in accordance with several embodiments of the invention.

FIG. 3A is a partially schematic, cross-sectional illustration of a substrate prior to having an interconnect structure formed in accordance with an embodiment of the invention.

FIGS. 3B-3E illustrate a process for forming a via suitable for receiving conductive material in accordance with an embodiment of the invention.

FIGS. 4A-4K illustrate a process for disposing a conductive material in the via in accordance with an embodiment of the invention.

FIG. 5 illustrates an interconnect structure having a reduced number of discrete layers, and an increased grain size uniformity in accordance with another embodiment of the invention.

FIG. 6 illustrates an imaging device that includes through-wafer interconnects configured in accordance with an embodiment of the invention.

DETAILED DESCRIPTION A. Overview/Summary

The following disclosure describes several embodiments of methods for forming through-wafer interconnects, and devices formed using such techniques. One such device includes a microfeature workpiece or substrate having a via with generally non-conductive wall portions. The wall portions are spaced apart by a width of the via, and the via has a length (generally transverse to the width) of at least 100 microns or more. A conductive material is disposed in the via and the conductive material has a generally uniform grain structure across the width of the via. In particular embodiments, the conductive material is disposed in the via without a seed layer located in the via.

A method for forming a microelectronic device in accordance with another embodiment of the invention includes forming a via in the microelectronic device, with the via having a width and a length generally transverse to the width. The length can be approximately 100 microns or more. The method can further include disposing a conductive material in the via while the via is exposed to a supercritical fluid. For example, the method can include combining a metal-containing precursor with a supercritical carbon dioxide solvent. The conductive material can be disposed in such a manner as to have a generally uniform thickness over the length of the via in a direction transverse to a sidewall of the via.

A method in accordance with still another aspect of the invention can include forming a via in a substrate and disposing an organic material (e.g., a photoresist material) on a surface of the substrate and in the via. The method can further include removing at least a portion of the organic material by exposing the substrate to a supercritical fluid. The method can further include disposing a conductive material in the via while the via is exposed to the supercritical fluid. In particular embodiments, disposing the conductive material can include introducing a conductive material precursor into the supercritical fluid, reducing the conductive material precursor by introducing an additional chemical specie or elevating a temperature of the supercritical fluid, or both, and causing the conductive material to precipitate from the supercritical fluid and occupy space in the via.

Specific details of several embodiments of the invention are described below with reference to CMOS image sensors to provide a thorough understanding of these embodiments, but other embodiments can use CCD image sensors or other types of solid-state imaging devices. In other embodiments, the invention can be practiced in connection with devices that do not include image sensors. Several details describing structures or processes that are well-known and often associated with other types of microelectronic devices are not set forth in the following description for purposes of brevity. Moreover, although the following disclosure sets forth several embodiments of different aspects of the invention, several other embodiments of the invention can have different configurations or different components than those described in this section. As such, the invention may have other embodiments with additional elements or without several of the elements described below with reference to FIGS. 2-6.

B. Methods for Forming Interconnect Vias and Conductive Structures

FIG. 2 is a flow diagram illustrating a process 200 for forming an interconnect structure in a microelectronic device. The process 200 can include forming a via in a substrate (process portion 202) and then disposing a conductive material in the via while the via is exposed to a supercritical fluid (process portion 204). Disposing the conductive material in the via can include one or more of several additional steps, identified in FIG. 2 as process portions 206-216. For example, the process 200 can include removing an organic material (process portion 206) before disposing the conductive material in the via. The organic material can include a residual photoresist material that remains after a prior masking process. The process 200 can further include introducing a conductive material precursor into the supercritical fluid (process portion 208) and chemically reducing the conductive material precursor (process portion 210). The process 200 can further include causing the conductive material to precipitate (process portion 212) into the via. The process of filling the via can then continue with the same conductive material precursor and in a supercritical fluid environment (process portion 214). In other embodiments, the via can be filled with additional conductive materials (process portion 216), either in a supercritical fluid environment or in an environment that does not include a supercritical fluid. Further details of the foregoing process steps and representative structures formed by executing those steps are described below with reference to FIGS. 3-6.

FIGS. 3A-3E illustrate a process for forming a via. Further details of this process are also provided in U.S. application Ser. No. 11/169,546, filed Jun. 8, 2005, entitled “Interconnect Vias and Associated Methods of Formation,” and incorporated herein by reference. FIGS. 4A-4K illustrate a process for forming a conductive interconnect structure in the via. As will be discussed in greater detail later with reference to FIGS. 4A-4K, aspects of the process may be conducted in a supercritical fluid environment. The structures formed using such techniques may be more structurally uniform and therefore may provide better and more reliable electrical conduction paths than existing structures.

FIG. 3A is a side cross-sectional view of a portion of an imager workpiece 300 at an initial stage before the interconnect structures have been formed. The workpiece 300 can include a substrate 301 with a plurality of imaging dies 320 formed in and/or on the substrate 301. The substrate 301 has a first side or surface 302 and a second side or surface 303. The substrate 301 is generally a semiconductor wafer, and the imaging dies 320 are arranged in a die pattern on the wafer. Individual dies 320 can include integrated circuitry 321, a plurality of terminals or bond sites 322 (e.g., bond-pads) electrically coupled to the integrated circuitry 321 with conductive paths 326, and an image sensor 312. The image sensor 312 can be a CMOS image sensor or a CCD image sensor for capturing pictures or other images in the visible spectrum. In other embodiments, the image sensor 312 can detect radiation in other spectrums (e.g., IR or UV ranges). The bond sites 322 shown in FIG. 3A are external features at the first side 302 of the substrate 301. In other embodiments, however, the bond sites 322 can be internal features that are embedded at an intermediate depth within the substrate 301.

FIG. 3B is a side cross-sectional view of the area 3B shown in FIG. 3A. In previous processing steps, a first dielectric layer 304 was applied to the first side 302 of the substrate 301, and a second dielectric layer 305 was applied over the first dielectric layer 304. The second dielectric layer 305 was then patterned and etched to expose the bond site 322. The dielectric layers 304 and 305 can be formed from a polyimide material or other nonconductive materials. For example, the first dielectric layer 304 and/or one or more of the subsequent dielectric layers can include parylene, a low temperature chemical vapor deposition (CVD) material such as tetraethylorthosilicate (TEOS), silicon nitride (Si₃N₄), silicon oxide (SiO₂), and/or other suitable materials. The foregoing list of dielectric materials is not exhaustive. The dielectric layers 304 and 305 may be but need not be composed of the same material. One or both of the layers 304 and 305 may be omitted and/or additional layers may be included in other embodiments.

After depositing the second dielectric layer 305, a mask 306 is applied over the second dielectric layer 305 and patterned as shown in FIG. 3B. The mask 306 can be a layer of resist that is patterned according to the arrangement of bond sites 322 on the substrate 301. Accordingly, the mask 306 can have an opening over each bond site 322.

As shown in FIG. 3C, a hole or aperture 327 has been formed through the bond site 322. The hole 327 can be formed using a wet etching process that selectively removes material from the bond site 322 but not the first dielectric layer 304. The first dielectric layer 304 can accordingly act as an etch-stop. In embodiments where the bond site 322 includes more than one type of metal, the etching process can be repeated until the hole 327 extends through the bond site 322.

Referring to FIG. 3D, the first dielectric layer 304 directly beneath the bond site 322 is etched to expose at least a portion of the substrate 301. The etching process for the first dielectric layer 304 can be different than the etching process for the bond site 322 to account for the different compositions of these structures. For example, the dielectric etching process can selectively remove material from the first dielectric layer 304 at a higher etch rate than from either the bond site 322 or the substrate 301. The dielectric etching process accordingly does not significantly alter the general structure of the bond site 322 or the substrate 301. In an alternative embodiment, the hole 327 can be etched through both the bond site 322 and the first dielectric layer 304 using a single etching process.

FIG. 3E illustrates a process for forming a via 350 in the substrate 301. The substrate 301 can be positioned in a plasma chamber 360 (shown schematically in FIG. 3E), where it can be supported on a cold chuck 361. The cold chuck 361 can control a temperature T in the chamber 360 and, more specifically, the temperature of, or at least proximate to, the substrate 301. The via 350 can then be formed in the substrate 301 using a plasma process, e.g., a deep reactive ion etching process. In a particular embodiment, the temperature T within the chamber 360 is controlled to cryogenic temperatures. For example, the temperature T can be controlled to be from about 100° C. to about 130° C. (173K to 143K). In other embodiments, the temperature T may be controlled to other levels, for example, levels at or above 71K (the temperature at which nitrogen liquefies).

The size and shape of the via 350 can vary depending on the particular application. For example, the via 350 can have an aspect ratio of about 1:1 or greater in some embodiments. The via 350 can extend by a distance of at least 150 microns from the first surface 302. In any of the foregoing embodiments, the orientation of a sidewall 351 of the via 350 can be controlled by controlling one or more process parameters (e.g., substrate temperature, ion type and concentration and/or others). For example, the overall shape of the via 350 can be tapered so that the sidewalls 351 form an angle A with respect to the normal axis N. The value of angle A can be from about 0° to about 5°, and in a particular embodiment, about 3°. The value of the angle A is exaggerated in FIG. 3E for purposes of illustration.

Referring next to FIG. 4A, a third dielectric layer 431 is deposited onto the workpiece 300 to line the sidewalls 351 of the via 350 within the substrate 301. The third dielectric layer 431 electrically insulates components in the substrate 301 from an interconnect that is subsequently formed in the via 350, as described in greater detail below. In one embodiment, the third dielectric layer 431 can be an aluminum-rich oxide material applied using a pulsed layer deposition process or another suitable low temperature CVD oxide. In another embodiment, the third dielectric layer 431 can include a silane-based oxide material, e.g., a low silane oxide. A low silane oxide process can be particularly suitable when the sidewall angle of the via 350 is greater than zero degrees. This process is compatible with the low temperature at which the via 350 is formed. In still further embodiments, the third dielectric layer 431 can include other suitable dielectric materials. Referring to FIG. 4B, a suitable etching process (e.g., a spacer etch) is used to remove the third dielectric layer 431 from at least a portion of the bond site 322.

Referring to FIG. 4C, a barrier layer 433 is then deposited onto the workpiece 300 over the third dielectric layer 431 so as to be in electrical contact with the bond site 322. The barrier layer 433 generally covers the second dielectric layer 305 and the bond site 322 in addition to the third dielectric layer 431. In one embodiment, for example, the barrier layer 433 is a layer of tantalum that is deposited onto the workpiece 300 using physical vapor deposition (PVD). The thickness of the barrier layer 433 is about 150 angstroms. In other embodiments, the barrier layer 433 may be deposited onto the workpiece 300 using other vapor deposition processes, such as CVD, and/or may have a different thickness. The composition of the barrier layer 433 is not limited to tantalum, but rather may be composed of tungsten or other suitable materials.

In at least some embodiments, a resist layer 406 can be applied to the workpiece 300 prior to adding conductive materials to the via 350. The resist layer 406 can protect surrounding structures from deposition of such conductive materials, and can be removed from the surfaces of the via 350 itself. In some cases, residual resist 407 can remain in the via 350, in particular, on the surfaces of the barrier layer 433. As discussed below, this residual resist material 407 can be removed as part of the process for filling the via 350 with conductive material.

Referring next to FIG. 4D, the workpiece 300 can be placed in a chamber 460 suitable for supporting a supercritical fluid 480. As used herein, the term supercritical fluid refers to a substance that is above its critical temperature and critical pressure, e.g., beyond a point where the distinction between liquid phase and gas phase exists. The supercritical fluid 480 can accordingly fill the via 350. In one aspect of this embodiment, the supercritical fluid 480 can act to remove any residual photoresist material 407 (FIG. 4C) or other organic material that may be contaminating surfaces of the via 350. In a particular embodiment, the supercritical fluid 480 can include carbon dioxide, and in other embodiments, the supercritical fluid 480 can include other constituents e.g., other non-polar solvents.

Once the supercritical fluid 480 is introduced into the chamber 460, a precursor gas containing conductive material can also be introduced into the chamber 460. For example, when copper is deposited in the via 350, the precursor gas can include Cu(tmhd)₂. In other embodiments, for example, when materials other than copper are disposed in the via 350, the precursor gas can include other constituents. In any of these embodiments, the conductive material can undergo a reduction reaction and can precipitate from the supercritical fluid 480 after an appropriate triggering event has been initiated. Such an event can include the introduction of an additional chemical specie, (e.g., a catalyst) or elevating the temperature of the supercritical fluid 480, or both. In particular examples, copper can be precipitated into the via by introducing hydrogen in the chamber 460 in the presence of Cu(tmhd)₂ and elevating the temperature of the workpiece 300. The temperature to which the workpiece is elevated can be about 200° C. or higher, depending on factors that include whether the copper is precipitated onto an existing seed layer or directly onto the barrier layer 433. The workpiece 300 can be heated above the ambient temperature in the chamber 460 via a heated chuck 461. The pressure within the chamber 460 can also be elevated, for example, to pressures up to or in excess of 200 atm. Further details of suitable constituents and process parameters are known in a general sense in the relevant art, for example, in an article by Blackburn et al. titled “Deposition of Conformal Copper and Nickel Films From Supercritical Carbon Dioxide” (Science, vol. 294, 5 Oct. 2001), incorporated herein in its entirety by reference.

As noted above, the foregoing technique can be used to dispose a seed layer 434 on the barrier layer 433 in the via 350. The seed layer 434 can be composed of copper or other suitable materials. The thickness of the seed layer 434 may be about 2000 angstroms, but could be more or less depending upon the depth and aspect ratio of the via 350. It is expected that forming the seed layer 434 in a supercritical fluid environment will cause the seed layer to form uniformly over the barrier layer 433. However, in some cases (e.g., when techniques other than supercritical fluid deposition are used to form the seed layer 434), the seed layer 434 may not uniformly cover the barrier layer 433, and the seed layer 434 may have voids 435 within the via 350. This can cause non-uniform electroplating in the via 350 and across the workpiece 300. When the seed layer 434 is deficient, it is preferably enhanced using a process that fills voids or noncontinuous regions of the seed layer 434 to form a more uniform seed layer. Referring to FIG. 4E, for example, voids 435 and/or noncontinuous regions of the seed layer 434 have been filled with additional material 436, such as copper or another suitable material. One suitable seed layer enhancement process is described in U.S. Pat. No. 6,197,181, which is incorporated by reference.

Referring next to FIG. 4F, a resist layer 407 is deposited onto the seed layer 434 and patterned to have an opening 408 over the bond site 322 and corresponding via 350. A first conductive layer 437 is then deposited onto the exposed portions of the seed layer 434 in the via 350. The first conductive layer 437 can include copper that is deposited onto the seed layer 434 in a supercritical fluid environment, in a manner generally similar to that described above. In the illustrated embodiment, the thickness of the first conductive layer 437 is about 1 micron. In other embodiments, the first conductive layer 437 may include other suitable materials and/or have a different thickness.

Referring to FIG. 4G, a second conductive layer 438 is deposited onto the first conductive layer 437 in the via 350. The second conductive layer 438 can include a wetting agent that facilitates depositing subsequent materials into the via 350. For example, the second conductive layer 438 can include nickel that is deposited onto the first conductive layer 437 in a supercritical fluid environment, generally similar to that described above. In such cases, a suitable nickel-continuing pre-cursor (e.g., NiCp₂) can be introduced into a supercritical CO₂ environment at suitable temperatures and pressures (e.g., 60° C. and 200 atm), and reduced with hydrogen. In the illustrated embodiment, the thickness of the second conductive layer 438 is approximately 3-5 microns. In other embodiments, the via 350 may be coated with other suitable materials using other methods, and/or the second conductive layer 438 can have a different thickness.

Referring next to FIG. 4H, a vent hole 441 is formed in the substrate 301 extending from a bottom portion of the via 350 to the second side 303 of the substrate 301. The vent hole 441 can be formed using a laser to cut through the substrate 301 from the second side 303 to the bottom of the via 350. The laser can be aligned with the via 350 and/or the corresponding bond site 322 using scanning/alignment systems known in the art. A suitable laser is the Xise200, commercially available from Xsil Ltd. of Dublin, Ireland. After forming the vent hole 441, it is generally cleaned to remove ablated byproducts (i.e., slag) and/or other undesirable byproducts resulting from the laser. For example, the vent hole 441 can be cleaned using a suitable cleaning agent, such as 6% tetramethylammonium hydroxide (TMAH): propylene glycol. In other embodiments, the vent hole 441 may not be cleaned. In alternative embodiments, the vent hole 441 can be a different size or shape, and may be formed using an etching process (e.g., a dry etch and/or a wet etch), a mechanical drilling process, a dicing or laser slot, or another suitable method.

In several embodiments, a temporary protective filling or coating 439 (shown in broken lines) can be deposited into the via 350 before forming the vent hole 441. The protective filling 439 can be a photoresist, a polymer, water, a solidified liquid or gas, or another suitable material. The protective filling 439 protects the sidewalls of the via 350 from slag produced during the laser drilling process. The slag can negatively affect the process of plating nickel onto the seed layer and/or wetting a conductive fill material in the via 350. The protective filling 439 can be removed after forming the vent hole 441.

Referring next to FIG. 4J, a conductive fill material 440 is deposited into the via 350 to form an interconnect 430. The interconnect 430 has a first end 442 proximate to the bond site 322 and a second end 443 at the bottom of the via 350. The fill material 440 can include Cu, Ni, Co, Ag, Au, solder, or other suitable materials or alloys of materials having the desired conductivity. The conductive fill material 440 can be deposited into the via 350 using a supercritical fluid technique, generally similar to those described above.

The resist layer 407 can then be removed from the substrate 301 (as shown in FIG. 4J) and a suitable etching process can be used to remove the remaining portions of the seed layer 434 and barrier layer 433 on the first side 302 of the substrate 301. The first side 302 of the substrate 301 can be planarized using grinding, chemical mechanical planarization (CMP), and/or other suitable processes. The via 350 can initially be a blind via that can be made to extend entirely through the substrate by a backgrinding process described below with reference to FIG. 4K.

FIG. 4K illustrates the substrate 301 after material has been removed from the second surface 303 in a process that exposes the second end 433 of the interconnect structure 430. Accordingly, the second end 443 of the interconnect structure 430 can form a second bond site 444 to which the solder ball 411 can be attached for coupling the workpiece 301 to external devices. The interconnect structure 430 can extend for a significant distance in the substrate 301 from the first side 302. For example, the interconnect structure 430 can extend for at least 100 microns in some embodiments, and for 150 microns or more in other embodiments.

One feature of several of the embodiments described above with reference to FIGS. 2-4K is that the conductive materials can be disposed in the via 350 while the via 350 is exposed to a supercritical fluid. An advantage of this arrangement is that when the precursor gas is introduced into the supercritical fluid, it tends to be distributed uniformly throughout the fluid. Accordingly, the concentration of the conductive constituents in the supercritical fluid tends to remain uniform, even as the conductive material precipitates from the supercritical fluid. As a result, the concentration of the conductive material can remain generally constant throughout the via, even though the via may have a high aspect ratio (e.g., at least 1:1), and a significant depth (e.g., at least 100 microns). Because the concentration of the conductive constituents can remain generally constant throughout the via, the conductive constituents are expected to be generally uniform on the sidewalls and the bottom of the via as they precipitate from the supercritical fluid. This is unlike some existing arrangements, in which other deposition techniques, (e.g., electrodeposition and/or electroless deposition) may tend to deposit the conductive material in a non-uniform manner, as described above with reference to FIG. 1B. To address this problem, some existing methods rely on a forward (plating) step, followed by a backward (deplating) step to create a layer that extends through the via without being overly thick toward the via entrance. However, a problem with this technique is that it can be time-consuming, and may produce a scalloped or otherwise non-uniform layer.

Additional features of the supercritical fluid are that it generally has a low viscosity, low surface tension and high diffusivity. These characteristics also aid in providing uniform material deposition. Accordingly, these characteristics can improve the conductivity and robustness of the interconnect structures formed in a supercritical fluid environment.

In different embodiments, a manufacturer may elect to use aspects of the foregoing supercritical fluid deposition process for some or all of the conductive materials used to form the interconnect structure. For example, as described above, the supercritical fluid technique can be used to deposit the seed layer on the barrier layer. In some cases, depositing the seed layer using this technique is sufficient to provide the desired level of deposition uniformity for subsequent layers. In other embodiments, some or all of the additional layers may also be deposited using a supercritical fluid technique. For example, the copper and/or nickel layers may be deposited using such techniques. In other embodiments, other deposition techniques (e.g., techniques such as electroplating or electroless plating) may be used for these subsequent deposition steps. In still further embodiments, electroplating or electroless plating techniques may be used for the seed layer deposition, while supercritical fluid techniques are used to form subsequent layers. In still further embodiments, assuming a suitable precursor gas is available, the solder fill material can be deposited using a supercritical fluid technique.

In yet another embodiment, the supercritical fluid technique can be used to deposit material directly onto the barrier layer in a single, continuous process that proceeds at least until the via is filled. FIG. 5 illustrates the via 350 filled uniformly with a single fill material deposited in a single continuous step. In one aspect of this embodiment, the fill material can include copper, but in other embodiments, the fill material can include other conductive constituents. In certain of these embodiments, the fill material can be selected not to include solder, and can instead include more highly conductive materials with higher melting points. These materials, in addition to providing better performance through better conductivity, allow the workpiece to undergo further processing at higher temperatures. In many of the foregoing embodiments described with reference to FIG. 5, the fill material 440 can have a single, generally homogeneous crystal structure throughout the via 350 (e.g., across the width of the via 350 and throughout the depth of the via 350). This is unlike typical existing interconnect structures, which include one crystal structure for the seed layer and other crystal structures for the one or more subsequent conductive layers disposed on the seed layer. An advantage of the generally homogeneous crystal structure is that it may be less subject to disruptions and/or discontinuities which can affect the integrity of the interconnect. Another advantage is that disposing the conductive material in the via in a single continuous process can reduce the time and expense associated with forming the via, and can accordingly make the process for forming devices in which the via is positioned more cost effective.

FIG. 6 is a partially schematic illustration of a finished imaging device 610 configured in accordance with an embodiment of the invention. The imaging device 610 can include a die 620 having an integrated circuit 621 coupled to an image sensor 612, which can in turn include an array of pixels 670 arranged in a focal plane. In the illustrated embodiment, for example, the image sensor 612 can include a plurality of active pixels 670 a arranged in a desired pattern, and at least one dark current pixel 670 b located at a perimeter portion of the image sensor 612 to account for extraneous signals in the die 610 that might otherwise be attributed to a sensed image. In other embodiments, the arrangement of pixels 670 may be different.

A color filter array (CFA) 613 is positioned over the active pixels 670 a of the sensor 612. The CFA 613 has individual filters or filter elements 671 configured to allow the wavelengths of light corresponding to selected colors (e.g., red, green, or blue) to pass to each pixel 670 of the image sensor 612. In the illustrated embodiment, for example, the CFA 613 is based on the RGB color model, and includes red filters, green filters, and blue filters arranged in a desired pattern over the corresponding active pixels 670 a. The CFA 613 can further include a residual blue section 672 that extends outwardly from a perimeter portion of the image sensor 612. The residual blue section 672 helps prevent back reflection from the various components within the die 610.

The imaging device 610 can further include a plurality of microlenses 614 arranged in a microlens array 615 over the CFA 613. The microlenses 614 are used to focus light onto the initial charge accumulation regions of the image sensor pixels 613. Standoffs 673 are positioned adjacent to the microlens array 615 to support a transmissive element 616. The transmissive element 616 (which can include glass) is positioned to protect the microlens array 615 and other features of the die 620 from contamination. Lens standoffs 674 can be mounted to the transmissive element 616 to support a device lens 617. The device lens 617 is positioned a selected distance away from the microlens array 615 to focus light onto the microlens array 615 and ultimately onto the image sensor 612.

From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the invention. For example, while aspects of the invention have been described in the context of image sensor devices, these aspects may be applied to other devices as well. In particular embodiments, aspects of the invention have been described in the context of integrated circuit devices coupled to interconnect structures formed in accordance with particular methods. In other embodiments, the interconnect structures can be coupled to other microelectronic features, for example, capacitors or conductive lines. Aspects of the invention described in the context of particular embodiments may be combined or eliminated in other embodiments. Further, while advantages associated with certain embodiments of the invention have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited except as by the appended claims. 

1. A method for processing a substrate having a bond site at a first surface and a second surface opposite the first surface, comprising: forming a via in the substrate, the via having an opening proximate to the bond site of the substrate, a bottom portion in the substrate, and a sidewall between the opening and the bottom portion; contacting the sidewall of the via with a precursor of a conductive material in a supercritical fluid; depositing the conductive material on the sidewall of the via while the via is exposed to the precursor in the supercritical fluid, the conductive material being generally conformal to the sidewall of the via; forming a vent hole in the substrate with the conformal conductive material on the sidewall of the via, the vent hole extending from the bottom portion of the via to the second surface of the substrate; and filling the via with a fill material adjacent to the conformal conductive material after forming the vent hole.
 2. The method of claim 1 wherein: the fill material has a first end proximate to the first surface and a second end proximate the bottom portion of the via; the method further includes removing material from the second surface of the substrate until the second end of the fill material is exposed; and attaching a solder ball to the exposed second end of the fill material, the solder ball being in electrical communication with the bond site of the substrate via the fill material in the via.
 3. The method of claim 1 wherein depositing the conductive material includes performing a reduction reaction of the precursor in the supercritical fluid.
 4. The method of claim 1 wherein the precursor is a metal-containing precursor, and wherein depositing the conductive material includes combining the metal-containing precursor with a supercritical carbon dioxide solvent.
 5. The method of claim 1 wherein depositing the conductive material includes disposing a first conductive material on the sidewall of the via, and wherein the method further comprises disposing a second conductive material in the via adjacent to the first conductive material.
 6. The method of claim 1 wherein depositing the conductive material includes: exposing the via to the supercritical fluid; introducing the precursor of the conductive material into the supercritical fluid; reducing the precursor of the conductive material by introducing an additional chemical species, and/or elevating a temperature of the supercritical fluid; and causing the conductive material to precipitate from the supercritical fluid.
 7. The method of claim 1, further comprising removing an organic material from a surface of the sidewall of the via with the supercritical fluid before depositing the conductive material on the sidewall of the via.
 8. The method of claim 1 wherein depositing the conductive material includes depositing the conductive material while the precursor of the conductive material has a generally uniform concentration gradient in the supercritical fluid along a length of the via.
 9. The method of claim 1 wherein depositing the conductive material includes depositing the conductive material with a generally uniform grain structure.
 10. A method for processing a substrate, comprising: forming a via in a substrate, the via having an opening proximate to a bond site proximate a first surface of the substrate, a bottom portion in the substrate, and a sidewall between the opening and the bottom portion; precipitating a conductive material from a precursor in a supercritical fluid onto the sidewall of the via, the conductive material being generally conformal to the sidewall of the via; forming a vent hole in the substrate with the conformal conductive material on the sidewall of the via, the vent hole extending from the bottom portion of the via to a second surface of the substrate opposite the first surface; and filling the via with a fill material adjacent to the conformal conductive material after forming the vent hole.
 11. The method of claim 10 wherein precipitating a conductive material includes introducing the precursor of the conductive material into the supercritical fluid while the via is exposed to the supercritical fluid.
 12. The method of claim 10 wherein precipitating a conductive material includes: introducing the precursor into the supercritical fluid; reducing the precursor by introducing an additional chemical species, and/or elevating a temperature of the supercritical fluid; and causing the conductive material to precipitate from the supercritical fluid onto the sidewall of the via.
 13. The method of claim 10 wherein precipitating the conductive material includes performing a reduction reaction of the precursor in the supercritical fluid.
 14. The method of claim 10 wherein precipitating the conductive material includes combining the precursor containing a metal-containing constituent with a supercritical carbon dioxide solvent.
 15. The method of claim 10 wherein precipitating the conductive material includes combining the precursor containing a metal-containing constituent with a supercritical non-polar solvent.
 16. A method for processing a substrate, comprising: forming a via in a substrate having a first surface and a second surface, the via having an opening proximate to the first surface of the substrate, a bottom portion in the substrate, and a sidewall generally transverse to a width of the opening; introducing a precursor of a conductive material carried in a supercritical fluid to the sidewall of the via; precipitating the conductive material from the precursor in the supercritical fluid onto the sidewall of the via, the precipitated conductive material being generally conformal to the sidewall of the via; and after forming the conformal conductive material, forming a vent hole in the substrate extending from the bottom portion of the via to the second surface of the substrate.
 17. The method of claim 16, further comprising filling the via with a fill material adjacent to the conformal conductive material after forming the vent hole.
 18. The method of claim 16, further comprising maintaining a generally uniform concentration of the precursor in the supercritical fluid in the via as the conductive material is precipitated from the precursor.
 19. The method of claim 16 wherein: forming the via includes forming a via having a length of approximately 100 microns or more; and the method further includes maintaining a generally uniform concentration of the precursor in the supercritical fluid along generally the entire length of the via as the conductive material is precipitated from the precursor.
 20. The method of claim 16 wherein: forming the via includes forming a via having a length of approximately 100 microns or more; the method further includes maintaining a generally uniform concentration of the precursor in the supercritical fluid along generally the entire length of in the via as the conductive material is precipitated from the precursor; introducing the precursor includes introducing a precursor containing at least one of nickel and copper; precipitating the conductive material includes introducing hydrogen into the supercritical fluid and reducing the precursor of the conductive material with the introduced hydrogen. 